You have probably already sorted this out since the post is old but here is what you need to do anyway, might be helpful for someone.
var fref:FileReference = ...
//First add a handler for the complete data event
//Then implement your handler
private function uploadCompleteData(evt:DataEvent):void
//The evt.data contains your required response data
i know it's been a while
but - is it possible for you to show a script which demonstrate how a filereference can point to a cfc function (and pass aditional parameters...) ?
it would REALLY help some of us